With the development of society and constant progress of science and technology, electric bicycles and digital electronic products like mobile phones have currently become the main means of transportation and necessities in people's daily life. Such devices or products commonly use batteries for power supply, and people get used to using the tools or devices in the daytime and charging them at night, so charger devices are commonly in power-on states for a long time. Some people place charger devices in power-on standby states for several days, dozens of days, or even all year around, causing the chargers to remain in meaningless energized states for a long time, which not only wastes energy, but also accelerates the aging of the charging devices and even causes safety accidents. Besides, the devices have specific charging time, for example, the full charging time of electric bicycles is generally 8 to 10 hours, and 2 to 3 hours are generally required for charging digital electronic products like mobile phones. Due to the limitations of people's living habits and conditions, the connection between chargers and the mains cannot be cut off in time when charging is completed. Meanwhile, since the current technology is not perfect enough to completely settle the issue of automatically cutting off electrical connection between a charger and a charged device, especially cutting off electrical connection to mains lines when charging is completed, no-load loss and meanwhile potential safety hazards exist.
Electronic devices of less than 100 W such as chargers and power adapters now commonly use off-line flyback switching circuits, and the circuits convert alternating currents of 85 V to 275 V provided by a power grid into direct-current voltages required by the electronic devices. In a normal working state, the loss of a flyback switching power supply mainly includes conduction loss and switching loss as well as control circuit loss. In a standby state, since the output current of the system is nearly zero, the conduction loss can be ignored, and the switching loss and the control circuit loss become the main system standby power consumption. Referring to FIG. 2, the standby power loss existing in the present application mainly includes start loss (R201, R202), absorption loss (R203, C201), core loss (T) of a high-frequency transformer, reverse recovery loss (D301) of an output rectifier tube, drive loss (R211), and switching loss (Q201). The standby power loss is a serious waste due to the particularity of the charger, that is, restart is not needed after completion of charging in a complete charging process.
Fire accidents frequently reported in newspapers or news media that are caused by charging of electric bicycles or digital electronic products like mobile phones always remind people of the importance of charging safety. Various charging protection apparatuses or devices have continuously come onto the market. Such charging protection apparatuses or devices play a positive role in reducing charging safety accidents. However, such protection apparatuses also have the following deficiencies: 1. Human participation is required, that is, the apparatus needs to be actively turned on or started by the user for operation, for example, the apparatus can be used only when a button switch is pressed for start, so the use is inconvenient. 2. A timing apparatus, where the timing apparatus is used for manually setting a time, and power is turned off when the time expires. Since the charging time is uncertain, that is, the charging time is different if the remaining capacity of the battery is different, the timing time can solve the power-off problem only by increasing the time. 3. Since current mainstream chargers commonly use high-frequency switching power transformer circuit structures (traditional iron-core transformers have gradually exited the market), there are technical difficulties in realizing the power-off function by controlling on and off of a high-voltage end using a low voltage of an output end, especially for control using a relay. Due to the volume of the relay, the problem of product miniaturization and microminiaturization cannot be solved, and therefore, it is almost impossible to use a relay on a mobile phone charger.